WE describe here a sugar and amino acid transport protein that has been isolated from a cell for the first time. It is a homogeneous protein subunit from the mucosai brush border of hamster jejunum that is involved in the Na+-dependent binding of actively transported D-glucose and L-histidine. Its molecular weight was estimated to be 59,000 by Sephadex G-75 gel filtration1, 56,000 by sodium dodecyl sulphate-acrylamide gel electrophoresis2,3, and 50,934 by sedimentation velocity analysis4,5. The presence of both D-glucose and L-histidine-binding sites on the same protein with a molecular weight of approximately 55,000 may account for some of the observed competitive inhibitory effects between active intestinal sugar and amino acid transport that have been reported6.